Among ink jet printheads of the above type, there is an example shown in FIG. 17 which is already known. In this conventional ink jet printhead, the glass plate 70 as a head substrate has a lower surface provided with a plurality of dented groove-shaped ink passageways 71 (only one passageway is shown for convenience of illustration) which are formed by etching. A lower opening 71a of each ink passageway 71 is closed by a diaphragm 80. The diaphragm 80 includes a thin glass plate 81 capable of deflecting and has a lower surface formed with a conductive layer 82 such as an ITO layer (tin oxide layer containing a small amount of additives, or indium oxide layer containing tin oxide). The conductive layer carries a piezoelectric element 83 attached thereto.
With such an arrangement, when voltage is supplied to the piezoelectric element 83, the thin glass plate 81 deflects concavely into the ink passageway 71, as shown by arrow a in FIG. 17. As a result, the volume of the ink passageway 71 is instantly reduced to inject the ink contained in the ink passageway 71 from a nozzle bore 84.
However, in the conventional ink jet printhead, the head substrate 70 is made of a glass plate 70 as is the diaphragm 80, and the dented groove-shaped ink passageway 71 is made by an etching process, thereby rendering the etching process to be very difficult to perform. Further, for the purposes of processing the glass plate 70 to have predetermined outer dimensions, there may be necessary to perform a sand-blasting operation for example, which will require cleaning in a later process. Further, the glass plate 70 is susceptible to a damage such as cracking, thereby requiring delicate handling. Therefore, with the conventional ink jet printhead, the manufacturing processes are very complicated, the production efficiency is low, so that there exists an inherent problem of incurring cost increase.
On the other hand, high density printing is needed also in the field of ink jet printheads. For realizing high density printing with the conventional ink jet printhead shown in FIG. 17, it is necessary to increase the disposition density of the ink passageways 71 as well as, accordingly, the disposition density of the piezoelectric elements 83 mounted on the diaphragm. Thus, it becomes very difficult to separately perform a wiring operation to each of the piezoelectric elements disposed with a high density so that power is supplied. In addition to the problem that the connecting operation of wires performed to each of a great number of piezoelectric elements becomes troublesome, it will be required to ensure a larger spacing for performing the wiring operation to prevent the wires for many piezoelectric elements from interfering with each other. As a result, with the conventional ink jet printhead, due to the difficulty of providing electrical connection, the printhead as a whole has to be increased in size to overcome the problem, while the production process becomes disadvantageously complicated, thereby resulting in cost increase.
Particularly, in a color ink jet printhead, a plurality of printheads are to be juxtaposed for separately injecting different color inks such as cyanogen, magenta, yellow, black and the like.
In such a printhead, if the above described arrangement of the conventional printhead is adopted, the wiring arrangement for the respective printheads become complicated as described above. Further, the wiring arrangement will disadvantageously become much more complicated, since it is necessary to unite the wirings of the respective printheads at a certain point for electrical connection to a desired control circuit.